The tax deadline this Friday is leaving only one alternative for taxpayers falling behind in their rush to complete their returns on time.

About 9 million Americans are expected to request extensions on filing their returns by April 15, according to the Internal Revenue Service.

“It gives you the breathing room to get things together, to get things done,” said IRS spokesman Eric Smith.

The IRS bases its estimate of the extensions that will be filed on last year’s figure, which was “in the same ballpark” as the number expected this year, Mr. Smith said.

Anyone who needs more time can file Form 4868, which will give them an extra four months to get their tax returns in to the IRS, until Aug. 15.

The one-page form requires only an estimate of earnings, but does not require further proof of income.

However, it does not suspend the requirement to pay a tax bill.

The IRS says taxpayers who know they must pay some amount should estimate their bill and send a payment with their Form 4868. Otherwise, they will be slapped with penalties and interest later.

“This is an extension of time to file information, not an extension of time to pay any federal taxes that are due,” said John Hewitt, chief executive officer of tax preparation company Liberty Tax Service.

For taxpayers unable to pay, filing an extension will avoid late filing fees, which are even worse than interest and penalties on the bill.

Late-filing fees cost 5 percent a month of the amount of tax owed, up to 25 percent of the total bill.

Only a portion of taxpayers seeking extensions can be accused of being procrastinators.

“People file extensions for many reasons,” said Kathy Burlison, an analyst for tax preparation company H&R; Block.

Typical reasons include delays in receiving records required to complete a tax return and late payment of dividends by corporations whose fiscal year might end in the spring.

A new poll from Internet firm Yahoo found that 54 percent of taxpayers are waiting until this month to file their returns.

Of the 19,000 people surveyed, 14 percent plan to wait until the April 15 deadline and 9 percent plan to file for an extension.

IRS Form 4868 can be downloaded from the Internet at www.irs.gov, then typing “4868” in the keyword “search for” line, then selecting “forms and publications” from the pulldown “within” menu below it. The IRS also has a special phone number for extensions at 888/796-1074.

H&R; Block offers suggestions for filing extensions:

 If you file for an extension now, pay now. Taxpayers should use a worksheet included with Form 4868 to estimate their taxes and send a payment in with their extension forms. Otherwise, they will be subject to an interest charge of 6 percent per year. If they pay less than the amount of tax due, they will be assessed penalties for late payment.

 Taxpayers have the option of paying by credit card. The IRS accepts most major credit cards without an additional fee. However, card processors charge convenience fees.

 If you are unable to pay, do not file an extension. Taxpayers who complete their tax returns by April 15, but cannot pay the bill, should send in the return and pay as much as they can. The IRS will send them a bill or notice for the balance due.

 Installment agreements with the IRS also are possible for people unable to make a lump payment. The IRS charges interest and penalties on the unpaid balance. There is a $43 fee to set up the installment agreement.

 Consider extending the extension. Beyond the first extension to Aug. 15, a second extension for an additional two months is available in some cases. Anyone seeking the second extension must give the IRS a good reason. They also must either file a Form 2688 or write to the IRS explaining why a hardship is preventing an earlier filing.

Other extensions are available for Americans living abroad.

Members of the military serving in combat get an automatic extension to 180 days from their last day in a combat zone to file a return and pay taxes. Other Americans abroad get an automatic extension to June 15 without filing any paperwork.